Zircon U-Pb Dating on Mesozoic Granitoids at Wulian,Shangdong Province

Zircon U Pb dating was carried out for four granitoid plutons at Wulian in the northwestern part of the Sulu orogenic belt, whose intrusion ages were not known for a long time and thus were often confused with adjacent granitoids of Neoproterozoic age. The present dating yields concordant ages of 123±4 Ma for amphibole monzonite at Dadian, 126±3 Ma for pyroxene monzonite at Qibaoshan, 116±4 Ma for miraolitic granite at Wulianshan, and 115±1 Ma for monzonitic granite at Maershan. The results show the occurrence of Early Cretaceous intrusions at ～115 Ma and ～125 Ma in the Sulu orogenic belt, being consistent with those coeval magmatic activity in the Dabie orogenic belt and the northeastern part of the Sulu orogenic belt. Although these Yanshanian granitoids occur in the Triassic collisional orogen between the Yangtze and North China plates, they belong to post collisional magmatism and were produced by partial melting of the subducted continental crust.